1. Field of the Invention
The present invention relates to a light emitting diode, and more particularly, to a facet extraction light emitting diode (LED) having a high light emitting efficiency, and a manufacturing method thereof.
2. Description of the Related Art
Recently, a light emitting diode (LED) utilizing a group III-V or group II-VI compound semiconductor material is largely used in a light emitting device for producing visible light. Also, such an LED is adopted for a light source of various products such as lightening boards, lightening devices, and LCD backlights. In a method to manufacture the semiconductor LED, an n-type semiconductor layer, an active layer and a p-type semiconductor layer are sequentially grown on a substrate to form a light emitting structure.
The typical semiconductor LED is structured to extract light from upper or lower surfaces but not a plane surface, i.e., a facet. However, the LED cannot exceed 15% in its light extraction efficiency without a separate technique such as photonic crystal, which, even if adopted, yields merely about 30% light extraction efficiency. Such low light extraction efficiency is attributed to light absorption in a crystal and light loss at an electrode as well.
As an alternative structure, a facet extraction LED has been proposed. The facet extraction LED is structured to extract light from a facet where the active layer is exposed. Here, a plurality of the facet extraction LED can be arranged to manufacture a smaller surface light source device. The facet extraction LED may be configured as a Separate Confinement Heterostructure (SCH) to trap light around the active layer. Yet, in the facet extraction LED, a light extraction face is smaller than other faces and thus travels a long distance in a crystal before being extracted. This increases light loss in the crystal and reduces light extraction amount, thereby lowering light extraction efficiency to 2% or less.
FIG. 1 is a perspective view illustrating a conventional facet extraction LED. Referring to FIG. 1, the facet extraction LED 10 includes an n-type semiconductor 13, an active layer 15 and a p-type semiconductor layer 17 sequentially formed on a conductive substrate 11. The n- and p-type semiconductor layers 13 and 17, and the active layer 15 constitute a light emitting structure. A p-electrode 18 is formed on the p-type semiconductor layer 17 and an n-electrode 19 is formed underneath the conductive substrate 11.
As shown in FIG. 1, light is extracted and emitted from a facet A where the active layer 15 is exposed. The facet A, if the greater amount of light is extracted therefrom than from other faces, serves as a light extraction face. However, the facet A for extracting light is smaller than other faces such as an facet B, upper or lower surface. That is, a width W of the light extraction face A along a plane direction of the active layer is smaller than a distance L between the light extraction face A and its opposing face. This causes light to propagate a longer distance in a crystal before being extracted outside the LED, thereby resulting in considerable light loss in the crystal.
After all, the conventional facet extraction LED 10 fails to assure sufficient light extraction efficiency or light emitting efficiency. Further, the surface light source device such as the LCD backlight manufactured using a plurality of the facet extraction LED suitably serves to miniaturize a product, however, without exhibiting sufficient brightness due to degraded efficiency of the LED 10. This as a result calls for the facet extraction LED improved in light extraction efficiency more significantly.